Bicomponent polycaprolactone/gelatin and polycaprolactone/collagen fibres were formed by electrospinning using two kinds of solvents: a representative of commonly used solvents with this polymer composition, highly toxic hexafluoroisopropanol (HFIP) and alternative, less harmful one, the mixture of acetic (AA) and formic (FA) acids. Both material types were subjected to investigations of structure and in-vitro cellular activity. Viscosity and Fourier transform infrared spectroscopy (FTIR) measurements shown that the type of solvent used influences the structure of solution and conformation of polymer molecules. In-vitro quantitative tests as well as cell culture morphology observations proved that materials electrospun with the use of ‘green’ solvents can yield similar results to those obtained by made with toxic ones. Slightly better cellular response to materials electrospun from HFIP can be explained by relatively well dispersed components within the fibre and more expanded conformation of molecules, resulting in better exposition of RGD (Arg-Gly-Asp) binding sites to cells’ integrin receptors.

Cartilage loss due to age‐related degeneration and mechanical trauma is a significant and challenging problem in the field of surgical medicine. Unfortunately, cartilage tissue can be characterized by the lack of regenerative ability. Limitations of conventional treatment strategies, such as auto‐, allo‐ and xenografts or implants stimulate an increasing interest in the tissue engineering approach to cartilage repair. This review discusses the application of polymer‐based scaffolds, with an emphasis on hydrogels in cartilage tissue engineering. We highlight injectable hydrogels with various micro‐ and nanoparticles, as they constitute a novel and attractive type of scaffolds. We discuss advantages, limitations and future perspectives of injectable nanocomposite hydrogels for cartilage tissue regeneration.

Approach. Injuries of the central nervous system (CNS) can cause serious and permanent disability due to limited regeneration ability of the CNS. Presently available therapies are focused on lesion spreading inhibition rather than on tissue regeneration. Recent investigations in the field of neural tissue engineering indicate extremely promising properties of novel injectable and non-injectable hydrogels which are tailored to serve as biodegradable scaffolds for CNS regeneration. Objective. This review discusses the state-of-the-art and barriers in application of novel polymer-based hydrogels without and with nanoparticles for CNS regeneration. Main results. Pure hydrogels suffer from lack of similarities to natural neural tissue. Many of the biological studies indicated nano-additives in hydrogels may improve their topography, mechanical properties, electroconductivity and biological functions. The most promising biomaterials which meet the requirements of CNS tissue engineering seem to be injectable thermosensitive hydrogels loaded with specific micro-and nanoparticles. Significance. We highlight injectable hydrogels with various micro-and nanoparticles, because of novelty and attractiveness of this type of materials for CNS regeneration and future development perspectives.

Despite progress which has been made in recent years in the field of cell-based therapies or cell scaffolds for cartilage regeneration, a lot of work still needs to be done. Scaffolds remain a great base for tissue regeneration. However, proper implantation procedures or post-treatment still await development.

In this review we summarize paths of cartilage treatment, especially focusing on cell scaffold design and manufacture. As well as the advantages and disadvantages of available or investigated methods and materials, especially focusing on cartilage scaffold design. We show the most promising directions and barriers in the creation of healthy tissue.

Electrospinning of chitosan blends is a reasonable idea to prepare fibre mats for biomedical applications. Synthetic and natural components provide, for example, appropriate mechanical strength and biocompatibility, respectively. However, solvent characteristics and the polyelectrolyte nature of chitosan influence the spinnability of these blends. In order to compare the effect of solvent on polycaprolactone/chitosan fibres, two types of the most commonly used solvent systems were chosen, namely 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and acetic acid (AA)/formic acid (FA). Results obtained by various experimental methods clearly indicated the effect of the solvent system on the structure and properties of electrospun polycaprolactone/chitosan fibres. Viscosity measurements confirmed different polymer–solvent interactions. Various molecular interactions resulting in different macromolecular conformations of chitosan influenced its spinnability and properties. HFIP enabled fibres to be obtained whose average diameter was less than 250 nm while maintaining the brittle and hydrophilic character of the nonwoven, typical for the chitosan component. Spectroscopy studies revealed the formation of chitosan salts in the case of the AA/FA solvent system. Chitosan salts visibly influenced the structure and properties of the prepared fibre mats. The use of AA/FA caused a reduction of Young's modulus and wettability of the proposed blends. It was confirmed that wettability, mechanical properties and the antibacterial effect of polycaprolactone/chitosan fibres may be tailored by selecting an appropriate solvent system. The MTT cell proliferation assay revealed an increase of cytotoxicity to mouse fibroblasts in the case of 25% w/w of chitosan in electrospun nonwovens.

Bicomponent polycaprolactone/gelatin and polycaprolactone/collagen nanofibers formed by electrospinning using various solvents were subjected to biodegradation and compared. Hexafluoroisopropanol (HFIP) was used as a reference solvent, while the second, alternative solvent system was the mixture of acetic acid (AA) with formic acid (FA). Biodegradation of investigated materials was manifested mainly by the gelatin leaching, including collagen which is indeed denaturated to gelatin during electrospinning, leading to nanofibers erosion. There was no molecular degradation of PCL during 90 days of biodegradation procedure as deduced from no change in the elongation stress at break. The rate of biopolymer leaching was very fast from all materials during the first 24 h of biodegradation, being related to surface leaching, followed by a slower rate leaching from deeper material layers. Mass measurements showed much faster biopolymer leaching from nanofibers electrospun from AA/FA than from HFIP because of strongly emulsive nature of the solution in the former case. Irrespective of the solvent used, the leaching rate increased with initial content of gelatin. The analysis of Young modulus during biodegradation indicated complex mechanism of changes, including biopolymer mass loss, increase of PCL crystallinity and partial gelatin renaturation.

Biological interaction between cells and scaffolds is mediated through events at surfaces. Proteins present in the culture medium adsorb on substrates, generating a protein adlayer that triggers further downstream events governing cell adhesion. Polymer blends often combine the properties of the individual components, for example, can provide mechanical as well as surface properties in one fibre. Therefore, mixtures of synthetic polycaprolactone and gelatin as a denatured form of collagen were electrospun at selected conditions and polymer weight ratios. Fibre morphologies and chemical properties of the surfaces were analysed. These scaffolds were seeded with human mesenchymal stromal cells and their viability was studied. Gelatin addition to polycaprolactone leads to a reduction in fibre diameter. A linear increase in gelatin at the fibre surface was observed in function of the weighed polymers, except for polycaprolactone/gelatin fibres incorporating equal weight ratios. Thereby, a depletion of gelatin at the fibre surface is stated for equally mixed polymers. The depletion of gelatin at the fibre surface is most probably due to hydrophobic interactions between hydrophobic segments of polycaprolactone and gelatin, affecting the spinning mechanism and thus fibre structure. Furthermore, polycaprolactone/gelatin blends show enhanced wettability properties compared to pure gelatin, at least partly due to molecular segregation. Results of in vitro studies reveal an increase in cellular viability and proliferation for cells cultivated on nanofibres containing gelatin, caused by the cell-attractive surface composition as well as the hydrophilic nature of the scaffolds. Contact guidance of cells seeded on parallelised fibres is observed, and DNA tests show evidently enhanced cell numbers on nanofibres containing 20 wt% of gelatin.

Polyamide 11/multi-walled carbon nanotubes nanocomposite fibers with weight fraction 2, 4, and 6 wt.% and diameter 80 μm were prepared with a twin screw mini-extruder. The morphology and degree of dispersion of the multi-walled carbon nanotubes in the fibers was investigated by using scanning and transmission electron microscopy. In turn, the molecular structure was indicated by using wide-angle x-ray scattering and correlated with thermal analysis. It was found that carbon nanotubes lead to the formation of α phase in the fibers and they show medial level of alignment within the length of the fiber. Mechanical analysis of the fibers shows that apart from the crystallinity content, the tensile strength is strongly dependent on the macroscopic defects of the surface of the fibers. Nanocomposite fibers based on polyamide 11 with carbon nanotubes can be used as a precursor for non-woven or woven fabrics manufacturing process.

The effect of electrospinning parameters on morphology, molecular, and supermolecular structure of polycaprolactone (PCL) fibers was analyzed, with respect to tissue engineering applications. Fibers morphology and structure are mainly determined by solution concentration and collector type. Applied voltage does not significantly influence supermolecular structure (crystallinity) and mechanical stiffness. There is correlation between changes in structure and proliferation of 3T3 cells as evidenced by in vitro study. Processing window of optimal scaffolds is relatively wide, however, variation of electrospinning parameters do not significantly affect their biological functionality.

Gelatin is one of the most promising materials in tissue engineering as a scaffold component. This biopolymer indicates biocompatibility and bioactivity caused by the existence of specific amino acid sequences, being preferred sites for interactions with cells, with high similarity to natural extracellular matrix. The present paper does not aspire to be a full review of electrospinning of gelatin and gelatin containing nanofibers as scaffolds in tissue engineering. It is focused on the still open question of the role of the higher order structures of gelatin in scaffold’s bioactivity/functionality. Gelatin molecules can adopt various conformations depending on temperature, solvent, pH, etc. Our review indicates the potential ways for formation of α-helix conformation during electrospinning and the methods of further structure stabilization. It is intuitively expected that the native α-helix conformation appearing as a result of partial renaturation of gelatin can be beneficial from the viewpoint of bioactivity of scaffolds, providing thus a much cheaper alternative approach as opposed to expensive electrospinning of native collagen.

Blends of polycaprolactone (PCL) and gelatine (Ge), being effective materials for tissue engineering strategies, were electrospun at various conditions and polymer weight ratios. The morphology, the supermolecular structure as well as the mechanical properties of resulting submicron sized fibres have been analyzed in relation to electrospinning conditions and PCL/Ge weight ratio. Compared to pure PCL, Ge addition leads to large reduction of fibre diameter and finally to changes of fibre morphology. For parallelised fibres collected on a rotating drum, preferred molecular orientation of PCL crystals is found. With increasing Ge content a general reduction of molecular orientation is observed. In addition, there is peculiar dependence of polycaprolactone crystallinity on the content of Ge, showing maximum at low Ge concentration (20%) as determined by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Such a trend can be explained by hydrophobic interactions in the system containing PCL, gelatine and water, being additional driving forces for crystallization of nonpolar PCL molecules. The presence of water within investigated blend systems has been evidenced experimentally using thermal gravimetric analysis (TGA). Young’s modulus of nonwovens, as determined by uniaxial tensile testing, indicates the effect of additivity of the stiffness of both polymers as well as the influence of preferred molecular orientation. Additional experiments were performed using collagen (Col) as a biopolymeric alternative to Ge. WAXS results show evidently amorphous structure of Col within the blended fibres, indicating strong tendency for denaturation of collagen into gelatine under the influence of hexafluoroisopropanol as a solvent.

The nature and efficiency of brain transmission pro-cesses, its high reliability and efficiency is one of the most elusive area of contemporary science [1]. We study information transmission efficiency by considering a neuronal communication as a Shannon-type channel. Thus, using high quality entropy estimators, we evaluate the mutual information between input and output signals. We assume model of neuron proposed by Levy and Baxter [2], which incorporates all essential qualitative mechanisms participating in neural transmission process.

Synthetic and natural polymers blends represent a new brand of materials with application in wound healing, scaffolds or drug delivery systems. Polycaprolactone/gelatin (PCL/Gt) blends were analyzed in terms of their miscibility. The PCL structure was investigated as a function of Gt content. Changes in the PCL spherulitic structure with Gt content were investigated by a polarizing-interference microscope. The analysis of the glass transition temperature (Tg) of both components as a function of PCL/Gt ratio by differential scanning calorimetry indicates that the system of polycaprolactone/gelatin belongs to a type of s.c. compatible system, being intermediate between miscible and immiscible systems. There is possibility of very limited miscibility of both components. Supplementary wide angle X-ray scattering results are presented.

The potential of polarizing-interference Pluta microscope for determination of optical birefringence of individual nanofibers formed by electrospinning was shown. This technique can be applied for measurements of fiber birefringence, practically at diameter above 300 nm. The molecular orientation of individual polycaprolactone (PCL) nanofibers was determined from birefringence assuming the same orientation of both phases, crystal and amorphous. The molecular orientation was determined using DSC crystallinity, crystal intrinsic birefringence calculated for the first time for PCL from bond polarizabilities as well as estimated value of amorphous intrinsic birefringence. Our results indicate that the birefringence and thus molecular orientation are strongly inhomogeneous along the nanofibers, reflecting a complex nature of forces acting during electrospinning process. The average molecular orientation is weak if any, being dependent together with fiber thickness and crystallinity on electrospinning parameters, like applied voltage, concentration and type of solvent. The obtained results indicate that the average molecular orientation displays similar dependence on applied voltage as fiber diameter. Relatively low melting temperature of electrospun nanofibers suggests low crystal size and/or high concentration of defects in crystals. This observation corresponds with low crystallinity and molecular orientation, indicating together relatively low degree of crystal ordering due to high rate of cooling and solvent evaporation during electrospinning, limiting thus crystallization process.

Electrospun nonwovens from PCL/gelatin and PCL/collagen structurally mimic native extracellular matrix and provide cells with chemical cues affecting them. Electrospinning of bicomponent nanofibres requires the use of a solvent which dissolves both of the polymers.
We have optimized the process of electrospinning of PCL/gelatin and PCL/collagen nanofibers based on the use of non-toxic, alternative solvents: acetic acid and formic acid (AA/FA) as previously described [1].
Bicomponent PCL/gelatin and PCL/collagen nanofibers were formed by electrospinning using the mixture of acetic acid and formic acid (9:1 w/w ratio), while hexafluoroisopropanol (HFIP) was used as a reference solvent. Nonwoven materials were subjected to cellular in vitro and biodegradation tests and compared.
All in vitro tests were performed using L929 mouse fibroblast cells. Cytotoxicity test was carried out on extracts and showed that all type of materials are not cytotoxic. Materials with 10% biopolymer content as well as made from PCL only underwent experiment in direct contact. Cells were cultured on materials for 3, 5 and 7 days and afterwards taken for SEM as well as fluorescent dying of nuclei and cytoskeleton. Obtained results proved that the addition of Arg-Gly-Asp (RGD) amino acid sequences from biopolymer, in comparison to pure PCL materials, facilitates cell adhesion and spreading on the surface of nonwovens regardless of solvent used in electrospinning.
PCL/gelatin and PCL/collagen nonwovens underwent biodegradation in PBS solution at 37°C. After different times, ranging from 1 to 90 days samples were subjected for comparative analysis via various methods.
Despite the fact that bicomponent nanofibers electrospun from alternative solvents have similar morphology to those electrospun from perfluorinated alcohols, they differ in the internal structure which seriously affects biodegradation process. Biodegradation of investigated materials is manifested mainly by the gelatin leaching, which leads to nanofibers erosion, particularly large for nanofibers spun from AA/FA.

Bicomponent polycaprolactone/gelatin nanofibers were formed by electrospinning as previously described [1] using a novel polymer – solvent system with solvents being alternative to the commonly used toxic solvents like fluorinated alcohols. PCL/Gelatin nanofibres were electrospun from the mixture of acetic acid (AA) with formic acid (FA) (90:10) and from hexafluoroisopropanol (HFIP), that was used as reference solvent. PCL/Gelatin nanofibres with polymers w/w ratios 9:1, 8:2 and 7:3, underwent biodegradation in PBS solution at 37°C. After different times, ranging from 1 to 90 days, they were rinsed in demineralized water and dried. Weight loss and FTIR tests were performed to assess the kinetics of gelatin leaching, while SEM imaging and hydrophobicity tests to show its depletion from the surface. DSC measurements were carried out to examine changes in fibres’ internal structure and uniaxial tensile testing to compare their mechanical properties. Morphology of PCL/Gt fibers obtained from AA/FA is similar to that obtained from HFIP. Despite similar morphology, the internal structure of nanofibers formed from alternative solvents is different, reflecting the emulsive nature of PCL/gelati n mixture in AA/FA solvents contrary to clear, transparent solutions in HFIP. This apparent difference affects strongly the kinetics of leaching of gelatin from bicomponent fibres and thus how their mechanical and bioactive properties are changing in time after placing in living organism. There is substantial difference in kinetics of gelatin leaching depending on solvent used. Mass measurements show much faster gelatin degradation in nanofibres electrospun from AA/FA than from HFIP . For instance, for PCL/Gt 7:3 samples, gelatin content loss is 85% for AA/FA and 68% for HFIP after 90 days. Moreover, irrespective of the solvent used, the degradation rate increases with initial content of gelatin and is the highest in the first 24 hours: 27% for AA/FA 9:1 and 67% for 7:3 and 13% and 32% for HFIP respectively. The observed changes can be explained by nonuniform distribution of gelatin within fibres spun form AA/FA due to emulsive character of solution. Comparison of SEM images reveals linear groove-like sites remaining after gelatin leaching on a surface of fibres spun from AA/FA solvent. Contrary to this, fibres spun from HFIP remain smooth which can be attributed to molecular dispersion of both components.

Cells sense subtract stiffness, elasticity and transduce that information into morphological changes and lineage specification. Polymer molecular order and mechanical properties, specially stiffness and elasticity indicate influence on cellular response during in- vitro study [e.g. Bershadskye et al 2013]. The aim of proposed presentation is to evaluate the effect of tailored crystallinity and mechanical properties of one- and bicomponent polymer films in terms of cells morphology and proliferation without changing other parameters. Polycaprolactone (PCL) and Gelatin (Ge) were used. As a solvents: Hexafluoroisopropanole (H), Acetic Acid (AA) were chosen. Two methods of foil preparation were analysed: forming from melt (onecomponent), forming from solution (one- and bicomponent).In both methods, the degree of crystallinity was modified mainly by the different type of PCL molecular weight, solvent type and/or annealing. Films were analysed using polarizinginterference microscopy allowing characterization of spherulities morphology. Degree of crystallinity was analysed by differential scanning calorimetry. Foils topography was analysed by atomic force microscopy, selected mechanical properties and hydrophilicity (contact angle) as the significant from the viewpoint of cellular activity were determined as well. L929 cells adhesion and morphology ware analysed by immunohistochemical staining for actin and nuclei. Cell activity and proliferation were analysed also. It is evident that conditions of PCL films preparation affect the morphology of spherulites. All samples were birefringent, indicating in general crystallinity, being different for particular samples. Maltese cross was observed in few samples. Crystallinity of PCL films determined from DSC measurements was in range 0,45-0,70 depending on solvent and polymer molecular weight used. Young Modulus strongly depends on Mw of PCL and Ge additive. L929 cells interact with subtract; morphology and proliferation degree change with crystallinity and elasticity of one- and bicomponet films.

Few research groups have highlighted the unexpected degree of cell proliferation depending on the degree of crystallinity of the substrate. Commonly used methods of forming three-dimensional scaffolds do not take into account crystallinity optimisation.
The aim of proposed presentation is to investigate polycaprolactone (PCL) substrate supermolecular structure effect, mainly crystallinity, on cells spreading, activity and proliferation.

Introduction In the case of semicrystalline polymers, crystallinity is the parameter determining their physical properties. Some research groups indicate influence of crystallinity on cells response during in- vitro study. Commonly used methods of three-dimensional scaffolds formation do not take into account crystallinity optimisation. The aim of proposed presentation is to evaluate the effect of molecular weight and solvent on crystallinity and crystal size in case of polycaprolactone (PCL) films. Methodology Material: PCL with Mn:10, 45 and 80k g/mol (Sigma Aldrich) was used. As a solvents: Hexafluoroisopropanole, HFIP (Iris Biotech GmbH.), Acetic Acid, AA and Dichloromethane, DCM (Avantor and Chempol respectively) were used. Methods: Films were prepared from the PCL with different molecular weight using various solvents differing in evaporation rate. Characterization: Films were analysed using polarizing-interference microscopy (MPI) allowing characterization ofspherulities morphology. Degree of crystallinity was analysed by differential scanning calorimetry (DSC) and comparatively bywide angle X-ray scattering (WAXS). Results and Discussion It is evident from MPI observations that conditions of PCL films preparation affect the morphology of spherulites. All samples were birefringent, indicating in general crystallinity, being different for particular samples. Sphorulities size depends on Mw and solvent type; sharp Maltese cross was observed on few samples. Crystallinity of PCL films determined from DSC measurements was in the range 0,45-0,68 depending on solvent and polymer Mn used. Generally crystallinity of films formed from DCM is lower than from AA as a result of lower boiling point of DCM. Additional annealing enables increase in crystallinity to 0,8. WAXS crystallinity correlates with values determined by DSC. Changes of full width of half maximum(FWHM) of crystal peaks indicate variations of crystal size and/or defects depending on molecular weight and solvent what correlates with MPI observations also. Conclusions spherulites shape and crystallinity are strongly dependent on Mn and solvent type. Structural parameters of films decide on Young modulus and elasticity in terms of applications

Influence of the crystallinity of the substrate on cell proliferation during in-vitro study was highlighted in few articles. Methods of forming 3-D scaffolds usually do not take into account crystallinity optimisation. The aim of proposed presentation is to investigate an influence of polycaprolactone (PCL) crystallinity on cells spreading, their activity and proliferation. PCL Mn 45k and Mn 80k g/mol were used. As a solvents: HFIP (H) and Acetic Acid (AA) were used. Two methods of foil preparation were analysed: -forming from melt (PCL45, PCL80) -forming from 10%wt solution (e.g. PH45, PAA45) Samples were analyzed using interfered-polarization microscopy (MIP) which allows to describe the morphology of spherolites (crystalline and amorphous phase). Degree of crystallinity was analysed by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Selected samples surfaces were O2 plasma treated to decrease hydrophobic properties of PCL. L929 cells adhesion and morphology were analyzed by immunohistochemical staining for actin and nuc lei. Cell activity and proliferation were analyzed. Morphology of spherolites was analyses using interfered-polarization microscopy (MIP). Analyses indicate changes in spherolites shape, size and also crystalline/ amorphous phase amount. Differences of crystallinity for PCL using different molecular weight were analysed by DSC and WAXS measurements. Decrease of contact angle was observed for O2 plasma treated samples. All PCL films were found as nontoxic for L929 cells. Differences in cells spreading, activity and proliferation degree were found. Modification of Mn, solvent and concentration of PCL enable film formation in wide range of crystallinity. L929 during in-vitro study interact with the PCL film. Crystallinity as part of the supermolecular structure influence on cells morphology.

Bicomponent poly(caprolactone)/ chitosan (PCL/Chit) nanofibers are a promising alternative for cartilage tissue regeneration. Chitosan is characterized by high structural similarity to the glycosaminoglycans (GAG) which naturally occur in the extracellular matrix (ECM). Its hydrophilicity is beneficial for cells adhesion and proliferation [1]. The amino groups in chitosan are responsible for the formation of polycations, which subsequently form compounds with natural and synthetic anions (proteins, lipids, synthetic polymers which are negatively charged) [2, 3]. Electrospinning of polycations with positive charge on the needle, is difficult due to the instability of the stream resulting from large repulsion force in the polymer jet [3]. Introduction of synthetic polymer molecules to the solution decreases interactions between the chains of chitosan and reduces the viscosity of the solution, so they are easier to form by electrospinning, as well as with negative charge on the needle [4 ]. A synthetic polymer, which is poly(caprolactone), improves mechanical properties of the fibers and the time of the hydrolytic degradation of the scaffold [4]. Nanofibers are excellent material for cell scaffolds used in tissue engineering because of high similarity of their morphology to native extracellular matrix (ECM) [1, 2]. From the viewpoint of cartilage tissue regeneration scaffold in the form of nanofibers is particularly justified due to naturally occurring network of polymer fibers (proteins and glycosaminoglycans) called aggrecans, in ECM of cartilage. Chondrocytes are connected with aggrecans [4]. Both, the structure and composition of formed nanofibers may affect the time in which cells will reach their proper morphology and undertake its functions [4]. In order to study cell behavior on electrospun PCL/chitosan nonwoven, fibroblasts L929 were cultured. Actin Green staining was conducted in order to imagine actin cytoskeleton of fibroblasts. To characterize, both fibers structure and cell morphology, SEM imagining was done. AFM imaging was carried to describe fibers topography and phase distribution. Also conductivity and viscosity of the PCL/chitosan solution with various polymer ratio was measured.